Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone.
Another process to produce phenol involves the hydroalkylation of benzene to produce cyclohexylbenzene, followed by the oxidation of the cyclohexylbenzene (analogous to cumene oxidation) to cyclohexylbenzene hydroperoxide, which is then cleaved to produce phenol and cyclohexanone in substantially equimolar amounts. Such a process is described in, for example, U.S. Pat. No. 6,037,513.
However, one problem in producing phenol by way of the cleavage of cyclohexylbenzene hydroperoxide is that the cyclohexanone and phenol produce an azeotropic mixture composed of 28 wt % cyclohexanone and 72 wt % phenol. Thus any attempt to separate the cleavage effluent by simple distillation results in this azeotropic mixture.
To obviate this problem, International Patent Publication No. WO2010/024975 proposes to integrate the cyclohexylbenzene production, oxidation and cleavage steps with a dehydrogenation step whereby at least a portion of the cyclohexanone is converted to additional phenol and hydrogen. The co-produced hydrogen is then separated from the phenol product and recycled to the benzene hydroalkylation step. It has, however, now been found that the separated hydrogen contains impurities, particularly water and C6 oxygenates, which, if not removed, may be detrimental to the catalyst employed in the benzene hydroalkylation reaction.
According to the present invention, there is provided a process for removing water and organic oxygenate impurities from a hydrogen stream, such as that produced in a cyclohexanone dehydrogenation process, wherein the hydrogen stream is subjected to a series of washing steps. The process provides a simple and effective method of removing the water and organic oxygenate impurities from the hydrogen stream thereby allowing the purified hydrogen to be employed in catalytic processes, such as benzene hydroalkylation.
U.S. Pat. No. 4,250,118 discloses an improved process for the preparation of cyclohexanone from benzene, wherein the benzene is hydrogenated in a gaseous phase in a hydrogenation zone to form cyclohexane; the cyclohexane is oxidized in a liquid phase to form a mixture containing cyclohexanol and cyclohexanone; the cyclohexanone is separated from this mixture and is catalytically dehydrogenated to form cyclohexanone and a hydrogen containing gas; and the resulting hydrogen containing gas is purified in a washing zone by washed with cyclohexane or benzene before the purified hydrogen gas is fed to the hydrogenation zone.